Vinyl chloride resins are widely used in the manufacture of various useful end products, including moldings, appliance cabinets, battery packs, etc. Unfortunately, unplasticized vinyl chloride resins used in the manufacture of rigid end products tend to have poor heat deformation characteristics. Consequently, they are unsuitable for use in certain areas of application where structural integrity under heat and load is of prime importance.
As reported in co-pending U.S. patent application, Ser. No. 209,843, filed by Jesse D. Jones and Edwin D. Hornbaker on Nov. 24, 1980, it has been discovered that blends of vinyl chloride polymers and copolymers of the styrene-maleic anhydride type can be formulated to have a number of superior performance characteristics, including increased resistance to heat deformation under load. The addition to these blends of impact modifier grades of: acrylonitrile and styrene grafted on polybutadiene or on styrene-butadiene copolymer rubber (ABS); styrene-methylmethacrylate grafted on polybutadiene or on styrene-butadiene copolymer rubber (MBS); and styrene-methyl methacrylate-acrylonitrile grafted on polybutadiene or on styrene-butadiene copolymer rubber (MABS), can provide articles with enhanced "toughness", i.e., an Izod Impact greater than about 0.8 lbs/in, and a heat deflection temperature measured at 66 psi of at least 75.degree. C. A high value for the heat deflection temperature measured at 66 psi is important as such value is required for thermoplastics which are to be used in the production of products subject to both heat and load stresses, e.g., television cabinets, battery housings, etc.
A more economical impact modifier, i.e., chlorinated polyethylene, can provide sufficient "toughness" to articles injection molded from blends of polyvinyl chloride and copolymers of the styrene-maleic anhydride type. However, the use of this material or the impact modifier for these blends results in a deleteriously low heat deflection temperature measured at 66 psi. Thus, while the ABS, MBS and MABS type impact modifiers provide suitable physical properties, their cost makes them not the materials of choice in commercial blends, while, on the other hand, chlorinated polyethylene, while cost effective, does not provide acceptable heat deflection temperatures.